The present invention is based on the knowledge that such a 3D image data record can be acquired from a number of 2D X-ray image data records, which are acquired with the aid of an X-ray radiation source and an X-ray radiation detector, which are moved one after the other into different rotational positions of a rotation in relation to a rotation axis, to acquire a 2D image data record in each instance. The so-called filtered back projection according to Feldkamp can then be used to calculate a 3D X-ray image data record.
In the present instance a 3D X-ray image data record is to be acquired for a moving object, for example the heart or the coronary arteries. Highly X-ray radiation-absorbent material is to be present here. This may be the metal in a catheter, a pacemaker cable or pacemaker electrodes but the highly X-ray radiation-absorbent material may also be a contrast agent introduced into the coronary arteries.
Two problems currently arise: while the 2D X-ray image data records are being acquired, the object is moving, making the acquisition of a 3D X-ray image data record difficult. Also the highly X-ray radiation-absorbent material produces artifacts in such a 3D X-ray image data record, these occurring in the form of stripes.
A number of designers have concerned themselves with supplying a 3D X-ray image data record for a moving object in recent times. For example EP 2 242 023 A1 deals with a method for reconstructing a three-dimensional final image data record with motion compensation. In this, as the 2D X-ray image data records are being acquired, associated information relating to a phase in the period of movement of the object is also acquired. Such a phase is referred to as a cardiac phase. It is then possible, for example using the method claimed in EP 2 242 023 A1, to calculate a 3D X-ray image data record from the 2D X-ray image data records. So-called motion fields can also be calculated for the individual phase intervals. For example the method for registering the images or back projection of the images of a phase interval to those of a reference phase interval makes it possible to determine which parts of the object are moving. This allows the motion fields to be derived. It is then possible also to derive the 3D X-ray image data record with the aid of all the 2D X-ray image data records from all the information relating to the movements.
A number of people have concerned themselves with the problem of suppressing artifacts, which result for example due to metal in the image object. It is thus known from Kalender et al., “Reduction of CT artefacts caused by metallic implants”, Radiology, August 1987, 164, pp. 576 to 577 to segment X-ray images, in other words to generate contours, which isolate regions of differing absorbency from one another. Segmentation takes place here in a 3D back projection. The segmented 3D back projection is then projected forward again. In the forward projection the metallic projection profile is replaced by a linearly interpolating segment in the, at the time of Kalender et al., single-line CT recordings. Later Müller and Buzug, “Intersection line Length Normalization in CT Projection Data” in Bildverarbeitung für die Medizin [Medical image processing] 2008, Springer-Verlag Berlin Heidelberg, proposed length-normalized line integral projection images to improve the interpolation result. Meyer et al., in their article “Normalized Metal Artifact Reduction (NMAR) in computed tomography”, in: IEEE Medical Imaging Conference, Record. 2009, Proceedings M09-206, October 2009, Orlando, Fla., then brought the length normalization method into general use.
However the known methods for eliminating metal artifacts always assume that the object is stationary.